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1. Field of the Invention
This invention relates to telecommunications networks, and more particularly, to hybrid network call delivery routing using a serving switching element point code and temporary destination location number.
2. Description of the Prior Art
As is the case for most businesses, telecommunications service providers desire to increase their profits. Typically, profits are increased by offering new products and services, and by reducing costs associated with providing an offered service. Communications service providers typically offer services on a very large scale, such as on a nationwide basis. In this environment, communications providers can substantially reduce costs by decreasing the number of messages sent between switching equipment when routing a call through the network. This cost reduction applies to all types of communications networks including the public switched telephone network (PSTN), cellular, and personal communications services (PCS) networks.
Communications elements communicate call signaling information using Signaling System #7 (SS7). A unique point code is assigned to each element in the signaling network. A point code is divided into a three-level hierarchy for efficient routing. In North America, the message transfer part level 3 point code consists of three 8-bit fields: Network ID, Cluster ID and Node ID. The SS7 message transfer part consists of three layers that together transfer messages across the signaling network. Message handling and network management is provided by message transfer part level 3. Messages received at level 3 are routed according to information in the routing label including the destination point code and originating point code. The destination point code specifies the network element which is to receive the particular message, and originating point code identifies the sender of the message.
Subscriber mobility is an important facet of personal communications services. PCS subscribers desire to be able to use their PCS and cellular phones wherever the subscriber travels. Location registration is the process of tracking mobile users. Databases called location registries assist in performing mobility management, and include a central home location registry and multiple visitor location registries. Current cellular standards and implementations use a two-tier hierarchy of databases to locate a PCS subscriber. Such techniques employ a central home location registry and multiple visitor location registries to maintain semi-permanent subscriber information; forwarding information is returned in response to location requests. In current implementations, when a new terminal (e.g., PCS phone or other device) is detected by a mobile switching center, it sends a registration notification message to its visitor location registry where the information (i.e., serving mobile switching center, terminal identification) is recorded and forwarded to the terminal""s home location registry. If the terminal was registered at another visitor location registry, the home location registry sends a registration cancellation request to that visitor location registry where the previous entry is deleted. This cancellation request is forwarded to the previous mobile switching center.
Call delivery is the process of locating mobile users and completing calls to them. During call delivery, the home location registry must query the listed visitor location registry which in turn queries the serving mobile switching center to obtain a temporary local directory number (TLDN) for routing to the destination mobile switching center. TLDNs cannot be allocated at location registration time due to the scarcity of numbers. More specifically, in current implementations, the originating switch (e.g., mobile switching center) sends a location request directly to the called party""s home location registry identified by the service provider of the called party""s universal personal number. The home location registry determines the party""s current visitor location registry based on a prior location registration sequence and sends a route request message to the visitor location registry. The route request message is forwarded to the visited mobile switching center. The mobile switching center allocates a temporary local directory number for the terminal and returns this through its visitor location registry to the home location registry where it is returned to the originating switch. The signaling traffic for such a scheme requires six signaling messages.
A method for improving the overhead associated with connecting a mobile call, including reducing the number of signaling messages required for routing the mobile call, is presented in Steven Michael Crowl, Non-Geographic User Locator Strategy for Personal Communication Service, A Dissertation in Computer Networking and Networking and Telecommunications, University of Missouri-Kansas City, Mar. 31, 1997 (hereafter xe2x80x9cCrowl 1997xe2x80x9d), and is hereby incorporated by reference. As the basis for routing mobile calls, Crowl 1997 proposes replacing the current use of a TLDN with a Signaling System #7 (SS7) point code identifying the serving network element. Using point code routing for call delivery, the call delivery process begins when a terminal sends a call request to its serving switch; the universal personal number of the destination terminal is included in the request. A database query is made to request the point code of the serving switch. The home location registry returns the point code of the mobile switching center serving the destination. The second part of the call delivery process routes the call to the destination mobile switching center based on the point code in the response. The point code of the called mobile switching center will be carried as a mandatory parameter in the initial address message (IAM). Intermediate switches will use this point code as a key to their routing tables to select the next switch in the path. As currently implemented in the network, the called party number is carried in the initial address message as a mandatory parameter for identifying the terminal at the destination switch. Such a methodology reduces the number of signaling messages required for call delivery from six to two. This message reduction increases signaling network capacity by two hundred percent, and reduces the transaction load on switching elements, drastically reducing unit cost.
However, the system contemplated and taught by Crowl 1997 requires each routing switch in the network to operate using point code routing, which is not feasible for existing communications networks. The cost to change each network element to use point code routing is substantial, and simultaneous cutting over of all network elements to use point code routing is unmanageable. In this regards, Crowl 1997 does not provide a cohesive strategy for deploying this technology in existing networks.
According to the invention, a method and apparatus are disclosed for hybrid network call delivery routing using a serving switching element point code and temporary destination location number. Moreover, the present invention expands the use of point code routing as contemplated by Crowl 1997 to include call routing for offering line number portability within the public switched telephone network.
Using a hybrid system as taught by the present invention, existing communications network can be migrated to advantageously use point code call routing. Moreover, the disclosed hybrid methodology does not require end-to-end use of point code routing. Rather, a provider""s network can transition the heavily trafficked network elements to reduce overhead and costs, while less heavily used network elements can continue to use destination phone number routing or be changed to support point code routing when the cost of its migration is justified.
The hybrid network of the present invention provides for call routing using a SS7 point code identifying the serving switching element for those elements that support point code routing, and TLDN routing for those network elements that do not support point code routing. When a path to a destination mobile switching center requires multiple hops (i.e., traverses through multiple network elements), the trunk group parameters for the next hop indicate whether the next network element can route based on a point code. If point code routing is available, the call signaling message is routed based on the point code value. Otherwise, a TLDN is requested and used. Because the current switch has the point code of the serving mobile switching center and the universal personal number (supplied in the initial address message) of the destination telephonic device, the switch can send a location request directly to the serving mobile switching center using this point code. The serving mobile switching center then allocates the TLDN as done by current systems, and returns the TLDN to the requesting switch. In an embodiment, the routing of the call then proceeds through the call completion using the TLDN, in which case the initial address message will be forwarded with the TLDN and without the serving point code parameter. In another embodiment, the initial address message will be forwarded with the TLDN and the serving point code parameter so that either the TLDN or the serving point code parameter can be used in routing the call through the rest of the network. In an embodiment, if the originating switch does not support point code routing (or selectively chooses not to use point code routing), the call can be routed first using a TLDN, with other network elements routing the call using point code routing. The present invention further provides that the type of call routing used can change between point code and TLDN routing at any network element.
An embodiment of the present invention includes a method for operating a communications network to provide call routing based on a serving network element point code and a temporary location directory number (TLDN) from a first switching element to a third switching element, the method comprising the steps of: the first switching element, supporting point code routing, receiving a call routing request having the serving network element point code; the first switching element routing the call based on the serving network element point code to a second switching element supporting point code routing; and the second switching element routing the call based on the TLDN to a third switching element not supporting point code routing. Preferably, the method further comprises the first switching element querying a database server to receive the serving network element point code. Preferably, the method further comprises the second switching element querying a serving switching element to receive the TLDN. Preferably, the method further comprises the second switching element querying a database server to receive the TLDN. Preferably, the call is a mobile wireless call. Preferably, the call is associated with a line number portability service.
An embodiment of the present invention includes a method for operating a communications network to provide call routing based on a serving network element point code and a temporary location directory number (TLDN) from a first switching element to a third switching element, the method comprising the steps of: the first switching element, supporting point code routing, receiving a call routing request having the serving network element point code; the first switching element routing the call based on the serving network element point code to a second switching element supporting point code routing; the second switching element routing the call based on the TLDN to a third switching element not supporting point code routing; the third switching element routing the call based on the TLDN to a fourth switching element supporting point code routing; and the fourth switching element routing the call based on the serving network element point code to a fifth switching element supporting point code routing. Preferably, the method further comprises the first switching element querying a database server to receive the serving network element point code. Preferably, the method further comprises the second switching element querying a serving switching element to receive the TLDN. Preferably, the method further comprises the second switching element querying a database server to receive the TLDN. Preferably, the call is a mobile wireless call. Preferably, the call is associated with a line number portability service.
An embodiment of the present invention provides for a method for operating a communications network to provide call routing based on a serving network element point code and a temporary location directory number (TLDN), the method comprising the steps of: a first network element supporting point code routing receiving a phone number of a called communications device; the first switching element querying a routing database using the phone number and receiving reply containing a serving network element point code; the first network element routing the call based on the received serving network element point code to a second network element supporting point code routing; the second network element querying a network element and receiving the TLDN; and the second network element routing the call based on the received directory number to a third network element. Preferably, the third network element is the serving network element.
An embodiment of the present invention provides for a hybrid communications network containing call switching elements, the hybrid communications network comprising: a first switching element for receiving a call having an associated serving network element point code and routing the received call based on the serving network element point code; a second switching element connected to the first switching element for receiving and routing calls based on either temporary location directory number (TLDN) or the serving network element point code; and a non-point code routing switching element connected to the second switching element for routing calls received from the second switching element based on the TLDN. Preferably, the connection between the first and second switching elements includes at least one switching element. Preferably, the connection between the second and non-point code routing switching elements includes at least one switching element. Preferably, the hybrid communications network of claim 15, further comprises a database server containing a set of point codes, wherein the first switching element queries the database server to receive the serving network element point code.